1. Field
Embodiments of the present disclosure pertain to polymer compositions suitable for high temperature service and, in particular, to particle toughened polymer compositions comprising a plurality of toughening particles and prepregs and composites formed therefrom.
2. Description of the Related Art
Laminated polymer matrix composite structures (PMCs) are widely used in a number of applications. For example, composite structures are being increasingly used in high performance aerospace applications. PMCs combine selectively oriented fibers that are enveloped in a surrounding polymeric matrix material. These composite structures exhibit good mechanical properties for their weight (e.g., strength, stiffness, toughness), as well as a wide service temperature window and ease of manufacture, making them well suited for aerospace applications.
Most polymer composites employ epoxy resins, owing to the good combination of mechanical properties wide temperature range, and ease of part manufacture afforded by epoxies.
However, some composite applications require high thermal durability in the finished composite and PMC parts used in extreme environments, such as high temperature applications, can lack adequate thermal durability. For example, epoxies may exhibit significant weight loss after long durations at high temperatures. Currently, there are no cost-effective polymer matrix composites that can withstand these extreme environments.
Polymers such as bismaleimides (BMIs) are gaining acceptance in aerospace applications that require service temperatures beyond the capability of epoxy resins. BMIs possess higher glass transition temperatures, Tg, than epoxies and exhibit relatively low weight loss during thermal ageing. BMIs also exhibit epoxy-like processing properties and high temperature durability. As a result, BMI resin-based composites possess good mechanical properties at temperatures within the range of about 149 to 232° C.
However, while the glass transition temperatures of BMIs are higher than those of epoxies, BMIs are also relatively rigid. As a result, BMI composites tend to exhibit poor damage tolerance and poor temperature cycling resistance to micro-cracking.
Furthermore, attempts to toughen BMIs through additives have proven relatively unsuccessful. For example, toughening agents typically employed in epoxy compositions, such as carboxyl-terminated butadiene acrylonitrile (CTBN), butadiene, and styrene type rubbers, have been observed to either reduce the Tg or promote high weight loss during thermal ageing. Thermal exposure may also reduce the effectiveness of these types of rubbers.
From the forgoing, then, there exists an ongoing need for tough composites capable of operating at high temperatures for extended duration.